title: Quantitative precipitin analysis of free and hidden RF IgM.
abstract: Quantitative precipitin analysis using rabbit IgG anti-human Fc mu was performed with 16 RF IgM, six macroglobulinaemic IgM and four normal IgM. Abnormal precipitin curves were obtained for all RF IgM, even when the latter were not readily demonstrated with conventional serological tests for RF, and for macroglobulinaemic IgM with sedimentation rates greater than 19S. These IgM formed significantly more precipitates with IgG anti-Fcmu in the antigen excess zone than did normal IgM, but the precipitin curves for the other zones were similar for all IgM. The underlying mechanisms of some of the reactions were studied and discussed. Because the divergence in the precipitin reaction for normal IgM and RF IgM was so pronounced, a model precipitin curve was constructed. This could be used to detect RF IgM, even when not readily demonstrable with conventional serological tests for RF, by direct analysis of serum. The results obtained for RF IgM suggested that the method might be applied to RF IgG and intermediate complexes comprised of IgG. The mechanisms demonstrated here might be used to develop immunological methods for routine use.
mesh_terms: D000818:Animals; D001172:Arthritis, Rheumatoid / Q000276:immunology; D006801:Humans; D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments; D007075:Immunoglobulin M; D011234:Precipitins; D011817:Rabbits; D012217:Rheumatoid Factor; D008258:Waldenstrom Macroglobulinemia / Q000276:immunology
chemical_list: D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments; D007075:Immunoglobulin M; D011234:Precipitins; D012217:Rheumatoid Factor